In recent years, there is widespread use of storage apparatuses including a plurality of mass storage devices such as Hard Disk Drives (HDDs). A storage system typically includes a plurality of storage devices, and a controller that controls access to these storage devices. There are also storage systems in which a plurality of controllers are provided to allow redundancy in the access paths to the storage devices. By providing redundancy in the access paths, the reliability of access to the storage devices may be improved.
Further, redundancy may be provided in the access path between each controller and the storage device by providing each controller with a second access path that goes through another controller between the controller and the storage device, in addition to a first access path that directly connects the controller and the storage device. For example, a conceivable configuration is such that in a case where each controller includes an expander that relays access to the storage device, each controller makes access to the storage device by using an access path through which the controller accesses the storage device via the expander within the controller itself, and an access path through which the controller accesses the storage device via an expander included in another controller.
In a case where each controller is configured such that its expander is activated with activation of a control unit that controls storage of data in the storage device, if the control unit in one controller is not activated due to some reason, it is no longer possible to access the storage device by using an access path that uses an expander connected to the control unit that is not activated.
Examples of related art are discussed in Japanese Laid-open Patent Publications Nos. 2006-155392, 2006-72636, 59-070145, and 2003-44178.